The light selective transmission filter is useful as a mechanical component, an electrical or electronic component, an automobile component, and the like, and particularly preferably used as an optical member. For example, a camera module includes an infrared shielding (cut) filter which shields infrared rays (especially infrared rays at a wavelength of more than 800 nm) which causes optical noise, thereby making an amount of absorption wave smaller than the amount of reflection wave. An infrared rays shielding glass which has an inorganic multilayer film formed by depositing a metal and the like on a glass filter and controls refractive indexes of respective wavelengths has been currently used. Optical members and the like have been recently downsized. For example, a digital camera module is mounted on a cellular phone. Therefore, a reduction in size of the optical members has been increasingly desired. Along with this, a reduction in size is needed for a filter for cutting infrared rays, used in a digital camera module and the like, or a lens unit having a lens and the like.
With respect to a near-infrared cut filter, for example, Japanese Kokai Publication No. 2006-30944 on pages 1 and 2 discloses a near-infrared cut filter having a near-infrared reflection film consisting of a dielectric multilayer film formed by alternately stacking dielectric layers with different refractive indexes on one surface of a transparent base material made of a thermal plastic resin having a specific glass transition temperature and a specific linear expansion coefficient, and at least one functional film selected from the group consisting of an equivalent refractive index film, a reflection preventing film, and a hard coat film on the other surface of the transparent base material. Further, Japanese Kokai Publication No. 2005-338395 on pages 1 and 2 discloses a near-infrared cut filter including a norbornene resin base material and a near-infrared reflection film.
However, if a film for reflecting or shielding infrared rays is formed by deposition, the deposition is performed at a temperature of several hundreds degrees or more. Therefore, the material for the base material needs to have heat resistance. Therefore, there is room for improvement in order to provide the material for the base material with sufficient heat resistance and form various materials for shielding infrared rays by various methods.
With respect to a lens unit, Japanese Kokai Publication No. 2005-309210 on pages 1 and 2 discloses an imaging lens which is constituted by disposing the first lens turning its convex surface to an object side and having main positive power, the second meniscus-shaped lens turning its concave surface to the object side, and the third lens functioning as a correction lens in this order from the object side to an image surface side, and in which a radius of curvature of the center of the surface (the first surface) on the object side of the first and second lenses and the focal distance of the entire lens system satisfy specific conditions. Japanese Kokai Publication No. 2006-18253 on pages 1 and 2 discloses a plate material-including optical member which is disposed on an optical axis and exhibits a specific function, wherein one or both surfaces of the plate material is/are set in aspherical shape, which corrects aberration of an optical system including such an optical member.
However, the technology on these lenses and optical members is insufficient for improvement in functions and added values, which has been currently developed in an optical field. There is room for improvement in order to provide an optical device with higher added values, for example, by downsizing components other than the filter correcting aberration of a lens or an optical system, thereby permitting a reduction in size of a lens unit.